In a system where multiple carriers may be used for UE operations simultaneously, the carrier assignment to each UE is important issue since the way to manage system carriers should be optimized to achieve maximal system performance and throughput. The situation may happen at the time of UE initial access to system, UE handover, carrier load balancing, multi-cell operation on specific carrier(s), per-UE traffic variation, and so on. During these cases, an eNB may need to reorganize the carrier utilization scheme of each UE so that specific carrier may be empty or managed to the target status, while UE have to retain the sustained service provision from the corresponding eNB(s). Multiple eNBs or cells may be responsible to this change (e.g., situation of CoMP operation).
However, in a system where multiple carriers may be used for UE operations simultaneously, a method of managing the carrier assignment has not studied yet.